A mother and father who murdered their daughter because she would not embrace their Pakistani culture were given away by a single nod.A body language expert has analysed footage of Iftikhar and Farzana Ahmed lying to the public about 17-year-old Shafilea's 2003 disappearance, claiming they were being racially victimised, for a documentary.It shows footage of an interview given by the parents, during which Iftikhar is asked if he had any involvement with his daughter's disappearance, to which he replies: 'Never. I couldn't even dream of it.'

Nine years after Shafilea disappeared, the truth finally came out in court - her father had stuffed a plastic bag in Shafilea's mouth, holding it there until she stopped breathing.

It was almost six months until her body was found in the River Kent in Cumbria, some 70 miles from the family home in Warrington, Cheshire.

Iftikhar and Farzana were convicted following evidence given by Shafilea's sister after she was arrested for setting up a robbery on her own parents.She told officers they had murdered her for failing to accept an arranged marriage, and told her siblings to keep quiet if they wanted to avoid a similar fate.

Her parents protestations of innocence came after they arrested along with five distant family members in the immediate aftermath of the tragedy.

They were released without charge, but following Alesha's testimony they were both jailed for life. A judge ordered both Iftikhar, then aged 52, and his 49-year-old wife to serve a minimum of 25 years in prison.How nodding can give the game away

In almost every culture in the world, nodding the head means 'yes' and shaking it from side to side means 'no', but the speed and frequency with which a nod is performed can carry different meanings.

A slow nod often means someone is listening, while a fast nod means the listener is saying that they have heard enough and wish to talk.

However it is wise to raise suspicions when someone shakes their head but actual says something positive, or nodding the head as they say something negative - as it could be a way of determining that they are lying.

And it appears that is what gave the game away for Iftikhar Ahmed, as determined by expert Cliff Lansley.

Shafilea's efforts to escape her parents' iron grip were thwarted by what criminologist Dr Aisha Gill called a 'catastrophic' communication breakdown during the trial, as social workers took her reluctance to make allegations of abuse at face value. During the interviews shown in the documentary, the parents brazenly claimed they were being victimised because they were Muslim.

Iftikhar looks directly into the camera when he says: 'They say "You're a Muslim family, Pakistani culture, this is the way you people are."

'That is the attitude they come up with, suggesting "you Muslim people do these things" - that we would kill our daughter.' And when pressed on the issue of an arranged marriage, they also strenuously denied any involvement.Her father adds: 'No, because the daughter does not want to be married yet. She was still under education, she wanted to make something of herself.

'Until such time she doesn't want anything to do with a marriage, which is fine.'